Digital multi-point electronic load weigh system

ABSTRACT

A digital multi-point electronic load weigh system is used with a railcar truck control unit to provide a digital all electrical/electronic system, which will perform the brake load weigh function for an electro-pneumatic brake system. The digital multi-point electronic load weigh system is primarily to be used with a distributed electronic control system using neuron style communication/control microprocessors. However, the digital multi-point electronic load weigh system can also be integrated with existing electro-pneumatic brake control components.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Pat. No. 6,120,109 entitledUniversal Pneumatic Brake Control Unit, which is assigned to theassignee of the present invention described and its teachings areincorporated herein by reference thereto.

FIELD OF THE INVENTION

The invention generally relates to a system for controlling the brakesof a railcar. More particularly, the invention pertains to a brakecontrol unit capable of being used with many different types ofelectropneumatic brake control systems for controlling the brakes on oneor more trucks of a railcar. Still more particularly, the inventionpertains to a device that electronically compensates for the weight ofthe load borne by a railcar truck in formulating the braking effort tobe applied to the wheels of that truck.

BACKGROUND OF THE INVENTION

A typical passenger transit or subway type train includes a locomotive,a plurality of railcars and several trainlines. The trainlines includeboth pneumatic and electrical lines most of which run from thelocomotive to the last railcar in the train. The main reservoirequalization (MRE) pipe is one such pneumatic trainline. It consists ofa series of individual pipe lengths. Secured to the underside of eachrailcar, one such pipe length connects via a coupler to another suchpipe length secured to a neighboring railcar. The MRE pipe is thusessentially one long continuous pipe that runs from the locomotive tothe last railcar. Charged by air compressors, which may be locatedthroughout the train, it is the MRE pipe that serves to supply air tothe various reservoirs, such as the supply reservoir, located on eachrailcar in the train.

One pneumatic trainline of particular importance to passenger transitand subway type trains is the brake pipe. It is used to convey to eachrailcar in the train an emergency brake signal when an emergencycondition arises. Of similar importance is the brake control trainlinethat is used to carry the brake command to each railcar in the train asdiscussed below. Contained within a protective conduit along with otherelectrical trainlines, the brake control trainline is similarly formedfrom individual conduits connected in series.

A locomotive for a passenger transit or a subway type train typicallyhas an electropneumatic brake control system such as the RT-5 BrakeControl System produced by the Westinghouse Air Brake Technology Company(WABTEC). Adapted or configured to fit the needs of various passengertransit authorities, each of the RT-5 style systems currently in servicefeature a master controller by which a train operator can direct theoverall braking and propulsive efforts for the entire train.

The master controller in the locomotive houses a handle, a computer andvarious other related components. The handle can be moved longitudinallyanywhere along its range of motion and into any one of severaldesignated positions. By moving the handle into the appropriateposition, a train operator can initiate, maintain or halt braking orpropulsion of the train. For example, from a position in which the trainis currently being propelled, moving the handle to what is referred toas the full service position causes a service application of the brakes.Similarly, when moved to the emergency position, the operator caninitiate an even faster type of braking referred to as an emergencyapplication of the brakes. There are other positions for the handlewhose purposes are beyond the scope of the present invention describedand claimed below.

Based on the positions of the handle, the computer of the mastercontroller can ascertain whether, and to what degree, the overallbraking or propulsive effort of the train should be reduced orincreased. A keyboard may also be used to permit the operator greateraccess to the brake equipment, allowing, for example, input of set-upparameters. Other known components may also be used to provide variousother signals to the computer.

Based on the inputs it receives and the software that dictates itsoperation, the master controller essentially controls the overalloperation of the brakes. For service braking, the master controllerformulates the brake command appropriate to current conditions andconveys it along the brake control trainline to each of the railcars inthe train. Through its brake command, the master controller can orderany action from a release of brakes to a service application of thebrakes or any degree of brake application in between those two extremes.

For emergency braking, a push-button type emergency valve in thelocomotive can be used to affect a drop in brake pipe pressure to anemergency level using both pneumatic and electrical meanssimultaneously. When push-actuated, the emergency valve provides a pathfor the brake pipe to vent directly to atmosphere. It alsosimultaneously deenergizes an emergency trainline thereby deenergizingone or more emergency magnet valves to further vent the brake pipe.

Alternatively, when directed by the master controller, an emergencybrake control valve on the locomotive could be used to decrease brakepipe pressure to the emergency level. By reducing the brake pipepressure to the emergency level, whether initiated from the locomotiveor from any other point in the train, this sends an emergency brakesignal along the brake pipe to all other railcars in the train.

On passenger transit and subway-type trains, the brake pipe is typicallyoperated according to a binary logic scheme. Normal operating pressurefor the brake pipe during non-emergency situations ranges from 130 to150 psi, the pressure to which it is charged via the MRE pipe. Thetransition point, or emergency level, lies at approximately 90 psi. Apressure of 90 psi or below indicates an emergency. It is this lowerpressure range that constitutes the emergency brake signal.

Each passenger transit railcar typically includes an electroniccontroller and two trucks, with each truck typically having two axles.In response to the brake command received from the master controller inthe locomotive, the electronic controller controls the operation of bothtrucks on the railcar. The electronic controller, however, has twocentral processing units (CPUs). Along with its associated interfaceequipment, each CPU controls the brake equipment of one truckindependently of the other truck. It does so based on the brake commandand various other inputs specific to the truck that it controls.

The brake equipment for a truck includes a pneumatic control unit andone or more pneumatically operated brake cylinders. Shown in FIG. 1, thepneumatic control unit typically houses an application magnet valve(AMV), a release magnet valve (RMV), a relay valve, an emergencytransfer valve (ETV), a variable load valve (VLV) and an air springpressure transducer. Used to convert the pressure received from a loadsensing system on the truck, the air spring transducer provides afeedback signal indicative of the load borne by the truck.

The relay valve typically takes the form of a J-1 relay valve or similartype valve. It is an air piloted device whose construction and operationare well known in the brake control art. It features a control portconnected to the ETV, a supply port supplied by the supply reservoir, anoutput port from which air can be directed from the supply reservoir tothe brake cylinder(s), and an exhaust port from which to vent the brakecylinder(s) to atmosphere. The pressure of the air impinging upon itscontrol port and the pressure of the air that the relay valve deliversto the brake cylinders will be approximately equal, though the airdelivered by the latter will be in much greater quantity than thatreceived by the former.

During non-emergency operation of the pneumatic control unit (i.e., whenbrake pipe pressure lies above the transition point), the ETV assumes anaccess state in which it connects the control port to both the AMV andRMV. The AMV when opened then allows air from the supply reservoir viathe VLV to reach the control port. The RMV when opened allows whateverpressure that impinges on the control port to be vented to atmosphere.

By selectively controlling the opening and closing of the AMV and RMVwhen the ETV is switched to the access state, the electronic controllercan control the magnitude of the pressure received by the control port.A brake cylinder control transducer, also a part of the pneumaticcontrol unit, converts the pressure at the control port to yet anotherfeedback signal. Along with other signals such as those relating tospeed, dynamic braking, wheel slip, the air spring feedback and others,this feedback signal is conveyed to the electronic controller to aid itin controlling each pneumatic control unit independently.

The electronic controller acts upon the brake command that it receivesfrom the master controller in the locomotive. Specifically, duringservice braking, each CPU formulates the exact amount of braking effortappropriate for its truck. It does this by processing the brake commandand the aforementioned other signals according to a brake controlprocess whose specifics are beyond the scope of the present inventiondescribed and claimed below. Operating in what can be referred to as aservice braking mode when its ETV is switched to the access state, thepneumatic control unit has its AMV and RMV magnet valves controlled bytheir corresponding CPU; each magnet valve being energizable by the CPUwith a field effect transistor (FET). By such control of the AMV and RMVmagnet valves, the CPU can control the flow of air from the supplyreservoir via the VLV and the AMV and RMV magnet valves to the controlport via the ETV. This produces at the control port of the relay valve alow capacity pressure corresponding to the amount of braking effortformulated for that particular truck.

The pneumatic control unit operates in what can be referred to as anemergency braking mode when its ETV is switched to the bypass state.Specifically, in an emergency, the ETV responds to the emergency brakesignal by pneumatically switching itself to the bypass state in whichthe AMV and RMV are cutoff from the control port. Air from the supplyreservoir is then allowed to flow via the VLV through the ETV directlyto the control port. Built at the control port of the relay valve inthis manner is a low capacity pressure capable of initiating anemergency application of the brakes on the truck.

In response to whatever low capacity pressure is impinging on itscontrol port, the relay valve provides to the brake cylinder(s) acorresponding pressure of high capacity. This compels the brakecylinder(s) to apply the brakes on the truck. The magnitude of thebraking force applied to the wheels is directly proportional to thepressure built up in the brake cylinder(s).

It is also well known that the braking effort sought to be applied towheels of a truck is often formulated to take into account the weight ofthe load borne by the truck through a process generally known as loadcompensation.

The variable load valve (such as that described in Operation &Maintenance Publication 4229-1 published by WABTEC) is an air piloteddevice whose construction and operation are well known in the brakecontrol art. The magnitude of the air spring pressure is indicative ofthe load that the truck is currently carrying. The VLV is designed tolimit the maximum pressure at which air from the supply reservoir isdirected to the control port of the relay valve. This maximum controlpressure level is proportional to the pressure that the VLV receivesfrom the air springs. For any particular level of air spring pressure,the VLV determines the maximum allowable pressure that will be suppliedto the control port of the relay valve in an emergency.

Regarding the combined operation of the VLV and the relay valve, whenthe pneumatic control unit operates in the emergency braking mode, itsETV is in the bypass state thereby bypassing the AMV and RMV valves andallowing air to flow from the VLV directly to the control port. Thecontrol port thus receives the maximum allowable pressure (i.e.,emergency brake control pressure) that the VLV can provide based on theload that the truck is currently carrying. The VLV is essentially set sothat the emergency brake control pressure for an empty railcar is X psiand, for a fully loaded railcar, it is (X+Y) psi. Though the emergencybrake control pressure can vary from X to (X+Y) psi depending on theload borne by the railcar at any given time, it will never decreasebelow X or increase beyond (X+Y).

The relay valve responds to the emergency brake control pressure bypressurizing the brake cylinder(s) to an emergency pressure level, alevel determined by the setting of the VLV. When operating in theservice braking mode with its ETV in the access state, the pneumaticcontrol unit has its AMV and RMV valves controlled by theircorresponding CPU. By manipulating the AMV and RMV valves according toaforementioned brake control process, the CPU produces at the controlport a lower capacity pressure (i.e., a service brake control pressure)corresponding to the amount of braking effort formulated for thatparticular truck. The magnitude of the service brake control pressure isdetermined by the CPU according to the aforementioned brake controlprocess. The relay valve responds to the service brake control pressureby pressurizing the brake cylinder(s) to a service pressure level, alevel determined by the CPU and one that will never exceed the emergencybrake control pressure setting of the VLV. In this manner, the VLVallows the truck to be braked at a relatively constant rate underfluctuating passenger loads.

The variable load valve has certain disadvantages when compared to thepresent invention. First, the VLV is inherently compromised in itsreliability due to its purely mechanical nature. It is a device thatnecessarily requires many parts, properly assembled and maintained, toperform its intended function, each part being subject to mechanicalwear and tear. Second, the VLV occupies a comparatively large amount ofspace in, and adds weight to, the system into which it is incorporated.The pneumatic piping that is necessary to connect the VLV to and fromthe pneumatic components in the system in which it is employed alsooccupies space in, and adds weight to, the system. Weight and space aretwo especially important factors in the rail industry where the costs offuel and the capability to transport cargo or passengers affect theviability of railroad and passenger transit authorities alike.

SUMMARY OF THE INVENTION

The present invention provides a digital multi-point electronic loadweigh system for performing a brake load weigh function on a truck of arail vehicle. Included in the system is a source of fluid pressure to beused for applying pressure to the brake on a truck of a rail vehicle.There is an air spring pressure means disposed on a truck of a railvehicle for receiving a plurality of predetermined air spring pressurelimits from a predetermined plurality of air springs pressure switches.A brake cylinder control means is used for receiving the plurality ofpredetermined air spring pressure limits for determining an emergencybraking condition exists, and generating a brake limit condition signal.There is a network communication and valve control means for receivingthe brake limit condition signal, for communicating a voltage signal toa common leg of the air spring pressure means in response to the brakelimit condition signal, and for generating an energization signal. Alsoincluded is an application valve for receiving the energization signaland for communicating a brake control pressure signal when energized.There is a relay valve for receiving the brake control pressure signal.The relay valve has a supply port connected to the source of fluidpressure, an output port connected to a brake cylinder of a truck, acontrol port for communicating the source of fluid pressure, and anexhaust port from which to vent such brake cylinder. The relay valveprovides, in response to the brake control pressure at its control port,a corresponding pressure to such brake cylinder thereby causing anapplication of such brakes on such truck. Also included is a releasevalve for exhausting pressure received from the control port of therelay valve when the release valve is open. A brake control means forconverting pressure received from a load sensing system to a feedbacksignal indicative of a load borne by such truck. There is also a meansfor granting a load compensation means exclusive control over theapplication and release valves such that the granting means responds toan indication of an emergency by disconnecting such controller unit fromthe application and release valves thereby giving the load compensationmeans exclusive control of the application and release valves wherebysaid load compensation means compensates for such load borne by suchtruck during emergency braking, and the granting means responds to anindication of a non-emergency by connecting such controller unit to theapplication and release valves by which such service braking on suchtruck is normally controlled with the load compensation means stillenabled to compensate for such load borne by such truck during suchservice braking. The present invention also provides a method forperforming a brake load weigh function on a truck of a rail vehicle. Themethod includes reading a network data packet from a sensor input meansfor determining a braking requirement. Upon determining if the brakingrequirement is an emergency brake condition it generates either a yessignal or a no signal indicative of the emergency brake condition. Themethod communicates the no signal to either a service brake or brakerelease means, and the yes signal to a means to determine anenergization pattern. Finally the method determines an energizationpattern.

OBJECTIVES OF THE INVENTION

It is, therefore, a primary object of the present invention to provide adevice that electronically compensates for the load borne by a railcartruck in formulating the braking effort to be applied to the wheels ofthat truck during an emergency. Another object of the present inventionis to provide an electronic brake load weigh device for use with a truckcontrol unit of a railcar to enable the truck control unit to compensatefor the load borne by the truck during braking operations. Yet anotherobject of the present invention is to provide an electronic brake loadweigh device that is far more reliable, smaller in size, lighter inweight, less likely to need maintenance and less costly than prior artmechanical apparatus used to perform the brake load weigh function on atruck of a railcar. In addition to the objects and advantages listedabove, various other objects and advantages of the present inventionwill become more readily apparent to persons skilled in the relevant artfrom a reading of the detailed description section of this document,particularly when the detailed description is considered along with thefollowing drawing figures and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a piping schematic of an electro-pneumatic brake controldevice, which uses a presently preferred embodiment of the digitalmulti-point electronic load weigh system of the invention.

FIG. 2 is an electrical schematic of an electro-pneumatic brake controldevice, which uses a presently preferred embodiment of the digitalmulti-point electronic load weigh system of the present invention.

FIG. 3 is a flow chart of a process for performing a load function usedby the digital multi-point electronic load weigh system of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Prior to proceeding with the more detailed description of the presentinvention it should be noted that, for the sake of clarity, identicalcomponents, which have identical functions have been designated byidentical reference numerals throughout the drawing Figures.

Reference is now made to FIGS. 1 and 2. Illustrated therein is apresently preferred embodiment of a digital multi-point electronic loadweigh system, generally designated 10, of a rail vehicle. The digitalmulti-point electronic load weigh system 10 for a rail vehicle comprisesa source of fluid pressure. The source of fluid pressure is either themain reservoir 12 of the brake pipe 14. There are three air springpressure switches, ASPS1, ASPS2, and ASPS3, designated 16, 18, and 22,respectively for receiving a plurality of air spring pressure limitsranging from about 60 psi to about 90 psi. Also included is a brakecylinder control device for receiving the air spring pressure limitsused for determining an emergency braking condition exists, convertingthe pressure into an electronic signal, and generating a brake limitcondition signal. There are eight possible patterns for determining anemergency braking condition, four defining a pressure level limitation,and four that indicate a fault in either the air pressure switches 16,18, and 22, or their interfaces. Referring now to Table 1 to indicatethe eight possible patterns: TABLE 1 Brake Cylinder Pressure Limit orASPS3 ASPS2 ASPS1 Fault Response 0 0 0 Limit Brake Cylinder Pressure to49.0 psi 0 o 1 Limit Brake Cylinder Pressure to 52.5 psi 0 1 0 FaultASPS2, or ASPS1; ASP1 Most Probable - Limit Brake Cylinder Pressure to55.8 psi 0 1 1 Limit Brake Cylinder Pressure to 55.8 psi 1 0 0 FaultASPS3, ASPS2, or ASPS1; ASPS3 Most Probable - Limit Brake CylinderPressure to 49.0 psi 1 0 1 Fault ASPS3, ASPS2, or ASPS1; ASPS2 MostProbable - Limit Brake Cylinder Pressure to 58.9 psi 1 1 0 Fault ASPS3,ASPS2, or ASPS1; ASPS1 Most Probable - Limit Brake Cylinder Pressure to55.8 psi 1 1 1 Limit Brake Cylinder Pressure to 58.9 psi

Also included is a network communication and valve control means 24 forreceiving the brake limit condition signal, for communicating a voltagesignal to a common leg of the air spring pressure switches 16, 18, and22 and for generating an energization signal. Connected to the networkcommunication and valve control means 24 is an application valve 26 forreceiving the energization signal and for communicating a brake controlpressure signal when energized, wherein the network communication andvalve control means 24 is a neuron style communication controlprocessor.

Also included is a relay valve 28 for receiving the brake controlpressure signal. Such relay valve 28 has a supply port 32 connected to amain reservoir 12, an output port 34 connected to line 36 leading to abrake cylinder of a truck (not shown), via either a manually orelectronically operated brake cutout valve 48 for maintenance purposes,a control port 38 for communicating the source of fluid pressure, and anexhaust port 42 from which to vent such brake cylinder.

Furthermore, the relay valve 28 provides, in response to the brakecontrol pressure at the control port 38, a corresponding pressure tosuch brake cylinder thereby causing an application of such brakes onsuch truck.

Also included is a release valve 42 for exhausting pressure receivedfrom control port 38 of the relay valve 28 when the release valve 42 isopen. The present invention further includes a brake control means forconverting pressure received from a load sensing system to a feedbacksignal indicative of a load borne by such truck, and a means forgranting a load compensation means exclusive control over applicationand release valves, 26 and 42. Such granting means includes a wheel sliprelease relay 44 that when energized closes a set of normally opencontacts and opens a set of normally closed contacts, each of thesenormally open contacts when closed completes one of a plurality ofconductive paths that electrically interconnects such controller unitwith the application and release valves, 26 and 42, each of the normallyclosed contacts when failing to close while the wheel slip release relay44 is de-energized signifies that a corresponding one of the normallyopen contacts mechanically associated therewith has failed to open.

The granting means responds to an indication of an emergency bydisconnecting such controller unit from the application and releasevalves, 26 and 42, thereby giving the load compensation means exclusivecontrol of the application and release valves, 26 and 42, whereby theload compensation means compensates for such load borne by such truckduring emergency braking, and the granting means responds to anindication of a non-emergency by connecting such controller unit to theapplication and release valves, 26 and 42, by which such service brakingon such truck is normally controlled with the load compensation meansstill enabled to compensate for such load borne by such truck duringsuch service braking. The granting means further includes a wheel sliplap relay 46 for interrupting a connection between the release valve 42and the wheel slip release relay 44 to energize the wheel slip releaserelay 44, such controller unit by energizing the wheel slip releaserelay 44 during an emergency permits such controller unit to control theapplication and release valves, 26 and 42, for at least a purpose ofcontrolling slipping of such wheels on such truck.

Reference is now made to FIG. 3. Illustrated therein is a flow chart ofthe presently preferred embodiment of a digital multi-point electronicload weigh system of a rail vehicle. The method in this embodiment ofthe digital multi-point electronic load weigh system for a rail vehicleincludes performing a brake load weigh function on a truck of a railvehicle. The method includes the steps of reading a network data packetfrom a sensor input means 52, determining a braking requirement 54,determining if the braking requirement is an emergency brake condition56 and generating either a yes signal or no signal indicative of theemergency brake condition. It also includes communicating the no signalto a service brake and brake release means 58, and the yes signal to ameans to determine an energization pattern 62.

The means to determine an energization pattern 62 determines theenergization pattern by performing a first lookup, and generating eithera first yes signal or a first no signal in response to the first lookupfunction. It also communicates the present state of the predeterminedair spring pressure switches 64, 66, 68, and 72 to the brake cylindercontrol pressure verification means 74, 76, 78, and 82 and the first nosignal to a means to determine a pressure switch fault 84. Thepredetermined air spring pressure switches 64, 66, 68, and 72 range fromabout 49 psi, about 52.5 psi, about 55.8 psi, and about 58.9 psi,respectively. Upon determining the energization pattern an applicationmagnet valve (not shown) is energized. The means to determine a pressureswitch fault 84 determines the nature of a pressure switch fault byperforming a second lookup function and generating either a second yessignal or a second no signal in response to the second lookup function.It is also responsible for communicating the present state of thepredetermined air spring pressure switches 86, 88, and 92 bycommunicating the second yes signal to the brake cylinder controlpressure verification means 94, 96, and 98, and the second no signal toa brake cylinder control means 102. The predetermined air springpressure switches 94, 96, and 98 range from about 49.0 psi, about 55.8psi, and about 58.9 psi, respectively. Upon verifying a fault conditionexists an application magnet valve (not shown) is energized.

While both the presently preferred and a number of alternativeembodiments of the present invention have been described in detail aboveit should be understood that various other adaptations and modificationsof the present invention can be envisioned by those persons who areskilled in the relevant art without departing from either the spirit ofthe invention or the scope of the appended claims.

1-12. (canceled)
 13. A method for performing a brake load weigh functionon a truck of a rail vehicle, said method includes the steps of: a)reading a network data packet from a sensor input means; b) determininga braking requirement; c) determining if said braking requirement is anemergency brake condition; d) generating at least one of a yes signaland a no signal indicative of said emergency brake condition; e)communicating said no signal to at least one of a service brake andbrake release means, and said yes signal to a means to determine anenergization pattern; and f) determining an energization pattern fromsaid means to determine energization pattern.
 14. A method forperforming a brake load weigh function on a truck of a rail vehicle,according to claim 13, wherein step (f) includes the steps of: a)performing a first lookup, and generating at least one of a first yessignal and a first no signal in response to said first lookup function;b) verifying a present state of said predetermined plurality of airspring pressure switches; c) communicating at least one of said firstyes signal to a first plurality of brake cylinder control pressureverification means, and said first no signal to a means to determine apressure switch fault; d) verifying a first plurality of predeterminedpressures; and e) energizing an application valve when saidpredetermined pressure is verified.
 15. A method for performing a brakeload weigh function on a truck of a rail vehicle, according to claim 14,wherein step (c) includes the steps of: a) performing a second lookupfunction and generating at least one of a second yes signal and a secondno signal in response to said second lookup function; b) verifying saidpresent state of said predetermined plurality of air spring pressure; c)communicating said second yes signal to a second plurality of brakecylinder control pressure verification means, and said no signal to saidbrake cylinder control means; d) verifying a second plurality ofpredetermined pressures, and a predetermined fault condition; and e)energizing said application valve when said predetermined faultcondition is verified.
 16. A method for performing a brake load weighfunction on a truck of a rail vehicle, according to claim 14, whereinsaid first plurality of brake cylinder control pressure verificationmeans is at least two.
 17. A method for performing a brake load weighfunction on a truck of a rail vehicle, according to claim 14, whereinsaid first plurality of predetermined pressures is at least two.
 18. Amethod for performing a brake load weigh function on a truck of a railvehicle, according to claim 15, wherein said second plurality of brakecylinder control pressure verification means is at least two.
 19. Amethod for performing a brake load weigh function on a truck of a railvehicle, according to claim 15, wherein said second plurality ofpredetermined pressures is at least two.
 20. A method for performing abrake load weigh function on a truck of a rail vehicle, according toclaim 16, wherein said first plurality of brake cylinder controlpressure verification means is four.
 21. A method for performing a brakeload weigh function on a truck of a rail vehicle, according to claim 17,wherein said first plurality of predetermined pressures is four.
 22. Amethod for performing a brake load weigh function on a truck of a railvehicle, according to claim 18, wherein said second plurality of brakecylinder control pressure verification means is three.
 23. A method forperforming a brake load weigh function on a truck of a rail vehicle,according to claim 19, wherein said second plurality of predeterminedpressures is three.
 24. A method for performing a brake load weighfunction on a truck of a rail vehicle, according to claim 21, wherein afirst predetermined pressure of said first plurality of predeterminedpressures is about 49 psi, wherein a second predetermined pressure ofsaid first plurality of predetermined pressures 52.5 psi, wherein athird predetermined pressure of said first plurality of predeterminedpressures is about 55.8 psi, and wherein a fourth predetermined pressureof said first plurality of predetermined pressures is about 58.9 psi.25. A method for performing a brake load weigh function on a truck of arail vehicle, according to claim 23, wherein a first predeterminedpressure of said second plurality of predetermined pressures is about49.0 psi, wherein a second predetermined pressure of said secondplurality of predetermined pressures is about 55.8 psi, and wherein athird predetermined pressure of said second plurality of predeterminedpressures is about 58.9 psi.